Formula 1: How Does a Diffuser Work?

Tomorrow, the whole Formula One season will be turned on its head.  Either six cars from Brawn GP, Williams, and Toyota will have their controversial diffusers found illegal which will cause them to be disqualified from the first two rounds of the world championship or they will be deemed legal forcing the other seven teams to play catch-up.

So before we get to Tuesday’s game changing meeting of the international court of appeal, I thought I would be a good idea to look at how a diffuser works on an F1 car and why the solutions the three teams under protest have developed are so far ahead of the competition.

How A Diffuser Works

Diffusers are essentially a raised area at the back of a car. In order to maximize the effectiveness of a diffuser, a car has to be run as low to the ground as possible. This causes the air trapped between the car and the ground to move rapidly to the rear. The diffuser section in the rear causes negative pressure at the back of the car because it has a bigger volume than the area that the air flowing into it is coming from. This negative pressure accelerates the air under the car which puts the whole underside of the car under negative air pressure. This creates a vacuum effect under the car which sucks it into the ground and creates downforce.


The picture of Ralf Schumacher’s car above is the best illustration of a pre-2009 F1 diffuser I could find. The diffuser section of the car starts at the leading edge of the rear tires and runs to the back of the car.  The FIA have tried to limit the effectiveness of the diffuser by mandating a 50mm step between the legality plank (the long wooden panel running along the length of the car) and the bottom of the sidepods. This greatly limits the ability of cars to accelerate the airflow underneath. If you look at the very back of Ralf’s car, you can see some small carbon fibre fins. These are used to clean the air flow at the back of the car. The cleaner the air coming out of the back of the car at the diffuser, the more efficient the diffuser is and more downforce is created.

The 2009 Diffuser


Above is a look at the diffuser of the 2009 McLaren MP4/24. The 2009 regulations say that the diffuser cannot be more than 1 meter across, the fins at the back (properly called strakes) and the total height of the diffuser cannot be more than 175mm high from the reference (legality) plank, and the diffuser is limited to 350mm deep starting at the rear axle. The diffuser that McLaren use in the picture above is their interpretation of a legal diffuser.  Ferrari, Renault, and BMW all have similar diffuser designs.

Williams FW31


Williams is running a “double-decker” diffuser.  As you can see on the picture, the middle part of the diffuser is bigger than the outside parts.  Also, there are two diamond shaped holes in the top-centre of the diffuser, right below the rear warning light.  These parts of Williams’ diffuser are designed to channel air from the top of the car and underneath into those holes and the large centre section to increase the efficiency of the diffuser.  The air funnelled in from the top of the car is supposed to increase the speed of the air flowing underneath the car, lowering the air pressure and creating more downforce.  The protesting teams also contend that the total height of the centre section is greater than the 175 mm from the reference plank allowed in the regulations.

Toyota TF109


If I was to take this at face value, I would imagine that this is the least controversial design of the three in question.  One controversial element is the vertical-running red winglets coming down off the rear warning light.  This effectively lengthens the diffuser in the middle section.  Toyota feels that those red pieces of bodywork are legal because they are part of the rear crash structure because that is what those pieces of bodywork are bolted to.  In order to further clean up the air coming off the diffuser, Toyota has a little winglet to that bodywork that I’ve highlighted with the yellow circle.  In addition to this, Toyota, like Williams, is channelling some extra air from above the car into through the diffuser using the section highlighted with the orange circle.

Brawn BGP001


Immediately, you can see that the curved centre section of the Brawn diffuser is unlike anything on any of the other cars.  This is the controversial part that is under protest.  You can’t really tell from this picture is that in the upper-left and upper-right areas of the central part of the diffuser have small holes, like the Williams, which feed air from the top of the car into the diffuser to accelerate the air.  This is part that is under protest.

One last point of interest before you go.


This is the Red Bull diffuser which is not under protest. If you look at the rear wing end-plates, you can see that they extend down next to the diffuser and along its full height. The endplates act effectively as strakes as they extend the width and depth of the diffuser. It’s not as controversial as the diffusers above but almost as liberal with their interpretation of the rules.

Now the question is what will happen tomorrow.  Regardless of who wins, Max Mosley’s cost cutting will be thrown out the window.  Teams are going to throw piles of money at the diffuser to quickly come up with a solution so they don’t fall behind the rest of the pack.

Photos from


7 thoughts on “Formula 1: How Does a Diffuser Work?

  1. Well said. I am almost getting sick and tired of all these regulations. Yeah, I guess there has to be limits, but this is down right sorry. As far as Ferrari bitching about the diffuser, I am surprised that Ferrari wasn’t the ones that started using these designs. The regulation is very vague and there is no way the court will rule in favor for Ferrari and others. I love the fact that Brawn team came out with very slick and simple design! And they have overwhelmed top performers. Yes, diffuser can give slight advantages on each corner (which is a huge deal in F1), but it doesn’t mean that diffuser alone determines the race.


  2. The FIA has now closed the loophole of the double diffuser for 2010.
    McLaren, Mercedes GP and at least two other teams have to make modifications to their diffuser prior to the Australian GP. The FIA is clamping down on teams exploiting the grey areas of the device, ironically Mercedes being one of these teams, in their former guise (Brawn) effetely introduced & won the championship with the same device.

    This I feel is outrageous, all the development that went on through the winter and the FIA feel that now they should implement an embargo against innovative use of the said device. The FIA constantly talk of cost reductions in F1, all that I can see in this situation is that now these four teams will have to spend unnecessary money now to modify these cars.

    I believe it is the FIA that is manufacturing escalated spending in F1. For example, two seasons in a row now all the teams have had to develop a car from scratch. 2009, full technical overhaul of the regulation, 2010, ban on in-race refueling. This meant that both seasons none of the teams could bring an evolution of their respective cars, spending tens of millions on development of new machinery.

    McLaren, Mercedes GP & Renault along with Force India will have to make these modifications prior to attending Albert park, with the later of those teams holding a significantly smaller budget than the prior three, we will all see who will be hit hardest. This is a team that was just showing real promise in there motor-sport campaign.


    • Jimmy,

      From what I understand the loophole to be closed is the excessive openings teams are using in their diffuser design to support the excuse of larger engine starters which give this additional aero performance. It sounds as if the double-decker diffuser isn’t to be banned entirely.

      It kills me to see the FIA impede innovation. However if they do not in this case, we wont have 4 teams that must throw out their design efforts, but we will have 9 that must put money forth in order to remain competitive. Needless to say, this would cost more to the sport in the end.

      These severe changes to regulations and spending limits were put in place in order to keep the sport interesting and improve viewership. I must say however, for all of the radical rework we’ve seen, efforts to more overtaking and exciting racing have backfired entirely. If Bernie gets his way with “shortcuts”, course designers will fucking kill him (unless they utilize existing short tracks or enforce mandatory pitting).

      Granted only race has gone down this season and teams are just getting used to this silly refueling ban. Hopefully someone with the intelligence steps up to offer a solution to all this year-after-year halfbaked nonsense.


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